The present invention relates to a power inverter and in particular, to a power inverter for electric vehicles or hybrid cars equipped with a plurality of components such as an engine, a revolving apparatus and the like, which are required to be small and light.
A conventional power inverter is disclosed, for example, in the specification of JP-A-11-163572. In this power inverter, a circuit case for accommodating a substrate having circuit elements mounted thereon is formed with a window for exposing the substrate, and an opening of a cooling case (opening for contact cooling) is closed by a surface portion of the substrate which is exposed from the window and is the reverse of the substrate surface on which the circuit elements are mounted. This specification further discloses a configuration in which a contact area (circuit-case side contact area) between the circuit case surrounding the substrate exposing window and the reverse surface of the substrate is arranged in such a manner that a liquid releasing gap in communication with an exterior is located between the above contact area and a contact area (cooling-case-side contact area) between the cooling case surrounding the opening for contact cooling and the reverse surface of the substrate. The gap in communication with the exterior is used to release a liquid if a seal is damaged.
The power inverter uses a configuration in which the cooling case and the circuit substrate are clamped together by bolts extending from the circuit substrate side. Thus, disadvantageously, the individual bolts must be sealed and if the sealed portions of the bolts are degraded, the liquid may leak to the circuit substrate side from the degraded sealed portions.
To solve this disadvantage, the circuit substrate and the cooling case (a heat sink) may be joined or integrated with each other. In this case, however, if the circuit is to be replaced due to defect thereof, it must be disassembled and dismantled together with the cooling case (heat sink). Thus, a new problem arises particularly with a power inverter for a hybrid vehicle using one enclosure to house a plurality of circuits; that is, maintenance for such a power inverter is difficult.
It is an object of the present invention to provide a power inverter that has an excellent cooling performance, prevents leakage, and allows size reduction of the apparatus and easy maintenance.
The above object is attained by a power inverter in which a plurality of power inverting semiconductor elements and exothermic electric parts are provided on insulated substrates, the insulated substrates are joined to a cooling plate (cooling substrate) constituting a lower lid of a case for accommodating the insulated substrates, an upper lid of the case is fixed to the cooling plate with screws or the like to constitute a power module, a heat sink having an opening is arranged in contact with a bottom surface of the cooling plate, a first seal portion is provided outside the opening and a groove is formed outside the first seal portion and in an outer wall of the heat sink, holes are formed in the groove at a plurality of locations so as to communicate with an outer surface side of the heat sink, and the heat sink and the cooling plate are clamped together outside the upper lid of the case and outside the groove formed in the heat sink.